"Hang on a minute," laughs Mr Mark Strong from behind a rack of luxury menswear, " I'll just get my clothes off and I'll be right with you." The actor is in a hurry, has been styled and primped for the camera, waylaid on the street by the iPhone paparazzi (who are often not quite sure where they know him from), but his good humour never misses a beat. Tall and slim, his bald head as smooth and tawny as a prize conker, Mr Strong has the gift of instant intimacy, talking to a stranger as if they were an old friend, putting all around him at ease.

Unravaged by the sags and creases so mercilessly exposed by HD on those of his vintage (he turned 50 in August), he has the perfect looks for a versatile character actor, a canvas to be imprinted with whatever role is required. After work he can go home to Queen's Park, unnoticed, and take his sons to the swings - quite unlike his great friend Mr Daniel Craig (godfather to Mr Strong's eldest). "It is very hard to keep a private life when you are famous on his level," he says sympathetically of his Our Friends in the North co-star. "I live a normal life. I travel on the tube. I keep my head below the parapet... it's the way I like it." An Arsenal FC season ticket holder, when his club won the double in 2002 he was jumping up and down outside the players' window (while Mr Ian Wright jettisoned bits of kit) when someone tapped him on the shoulder and intoned respectfully, "I loved you in The Iceman Cometh". He shakes his head in disbelief. "I mean really, there's a time and a place."

His latest quiet triumph is playing Detroit detective Frank Agnew in Low Winter Sun, AMC's 10-part thriller based on the 2006 Edinburgh-set Channel 4 drama of the same name, in which he played the same character. This time the mood is darkened by the hardcore edginess of a city on the brink, as Agnew and his partner, played by British actor Mr Lennie James, conspire to murder a corrupt colleague, unleashing a Greek tragedy of betrayal and reprisals. He was away from home for four and a half months, the latest in a stream of British exports (Mr Dominic West, Mr Damian Lewis, Mr Idris Elba) to play Americans for US TV. "I don't really understand it myself but I was told that American actors become too familiar for the small screen, which likes new faces."

When I last met Mr Strong more than a decade ago he was appearing in a Chekhov-Shakespeare double-bill in Mr Sam Mendes' final season at the Donmar Warehouse, drinking in the applause, utterly at home. He was single, driving a beaten-up old Renault, earning £350 a week. "I don't have a family to support," he told me, "I can afford to." Not long after that, he married the producer Ms Liza Marshall, and acquired not just two sons, now aged five and eight, but a new focus on earning a living: theatre wasn't going to pay the school fees. There followed eight years of solid name-building television performances (Harry Starks in The Long Firm, the Duke of Norfolk in Henry VIII, Prime Suspect and many more) before he finally stopped work for six months to wait for film offers. Using what he calls the "time-honoured entry ticket" of British actors into major studio pictures, acting nasty would become his forte.

I'd like it if my boys could see more of what I do but as morality tales dictate the good guy has to win, I have pretty much been horribly murdered in every film I've done

In Mr Guy Ritchie's Sherlock Holmes (2009) he played the Satanist Lord Blackwood, in Sir Ridley Scott's Robin Hood (2010) the traitorous Sir Godfrey and in Kick-Ass the brutal crime lord Frank D'Amico, whose death is avenged by his character's son in the new and no less grisly sequel Kick-Ass 2, which Mr Jim Carrey has refused to publicise in light of the Sandy Hook shooting. "I have to examine my own conscience and decide whether a film's violence is acceptable or not. If it is integral to the story and not violence for its own sake, I will do it." In Syriana his character's battering and torture of Mr George Clooney (think fingernails and pliers) left him wracked with guilt when he heard that the star had needed surgery for an agonising back injury afterwards. "He absolved me when I saw him at the last BAFTAs and reassured me he had fallen off a chair the wrong way."
Might it be time to play a nice guy? "No, the villains are too interesting to turn down... I wondered if I would be typecast but then I realised that I didn't care. I'd like it if my boys could see more of what I do but as morality tales dictate that the good guy has to win, I have pretty much been horribly murdered in every film I've done."

Though Mr Strong's toned physique works wonders for tailoring, he admits to little personal vanity: in mufti it's jeans, T-shirt, sweater... though with a penchant for handmade brogues. For a decade his only suit was an Alexander McQueen number he was given after a Vogue shoot with Ms Charlotte Rampling in which he reprised Harry Starks' gangster style. Latterly he relied on two suits donated by Mr Ozwald Boateng (they are the same size), but his professional wardrobe is quite another matter, one of obsessive interest. Frank Agnew sends mixed messages in a meticulous jacket and tie under a battered leather "man of the people" jacket; Hani in Sir Ridley Scott's Body of Lies, (2008) a Jordanian head of national security, was immaculate in Hackett's nifty jackets and elegant ties. "It defined him perfectly, to be so impeccably turned out in the middle of that dusty, murky world."

Zero Dark Thirty

In Robin Hood he wore seven layers, every one crucial for authenticity, and Lord Blackwood's leather frock coat, with a stand-up Persian lamb collar for full malevolent impact, was a camp-Gothic masterpiece. Does it go down well in Queen's Park residents' association meetings? He laughs. "If I wore it in real life I'd get kicked to death on the street." Nor does he mind sitting in make-up for hours while prosthetics are perfected for his ever-widening repertoire of sci-fi, superhero and comic-book creations.

He was so keen to play the evil Sinestro in Green Lantern (2011), with his massive forehead, pointy ears and bright red colour because in the original comics the character was based on Mr Strong's personal hero Mr David Niven, with a funny little pencil moustache. "It's not my job to make sure I look good on screen. I am trying to create a believable person." Though sometimes the preparation leaves him in good shape: for Frank Agnew, he was taught to jab at Detroit's Bad Boy Gym by the five-time world champion Mr Tommy "The Hitman" Hearns, a huge fitness boost.

It's not my job to make sure I look good on screen. I am trying to create a believable person

Even between filming, few of his days are free. There are voice-overs, publicity for forthcoming movies (next up: Before I Go to Sleep, co-starring Ms Nicole Kidman). He has handed over the narration of the family-tree show Who Do You Think You Are? to Ms Cherie Lunghi, though its producers have invited him to be a subject and research is underway on his family. "My wife is keen for me to do it because it would be lovely for our boys to know about my side of the family... but I'm in two minds."

The son of an Austrian mother and an Italian father he has never known, both his parents were young immigrants in London and he feels no resentment for what was a sometimes difficult childhood. In some ways, it gave him a useful edge: an outsider's perspective, the freedom to be his own man ("I probably wouldn't have switched from law to a drama degree if a father had been advising me"), not to mention the olive-skinned Mediterranean appearance that has made almond-eyed Arabs a speciality.

He is "desperate" to do theatre again but takes nothing for granted and, sweetly, seems taken aback by his own success. "I do my thing and it seems to appeal to people but this business is not a meritocracy. Why have I been successful? I have no idea. Luck plus talent gets you so far, but there is another element, more mysterious, that sustains it." Quite possibly it is just his plain niceness, the professional advantage of the rank villain who is really good fun to have around.